Disable filter applying for Truncate, Drop.

[sdanyliv]

Fixes #5417

[sdanyliv]

/azp run test-all

[azure-pipelines]

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[Copilot]

Pull request overview

This PR fixes issue #5417 where Truncate and Drop operations fail with an InvalidCastException when used on tables that have global query filters applied (e.g., soft-delete filters in EF Core). The root cause was that the builders directly cast the build sequence result to TableContext, but when query filters are present, the result is a SubQueryContext wrapper instead.

Changes:

• Disable query filters when building sequences in TruncateBuilder and DropBuilder, and use SequenceHelper.GetTableContext() to safely extract the table context instead of a direct cast.
• Refactor SequenceHelper.GetTableContext and GetTableOrCteContext to use the existing CreateRef helper method.
• Add a regression test that verifies Truncate and Drop work correctly on tables with complex query filters.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
Source/LinqToDB/Internal/Linq/Builder/TruncateBuilder.cs	Disable query filters during sequence building; use GetTableContext() instead of direct cast
Source/LinqToDB/Internal/Linq/Builder/DropBuilder.cs	Same fix as TruncateBuilder: disable filters and use safe table context extraction
Source/LinqToDB/Internal/Linq/Builder/SequenceHelper.cs	Minor refactoring to use CreateRef helper in GetTableContext and GetTableOrCteContext
Tests/Linq/Update/TruncateTableTests.cs	Adds regression test with a query-filtered entity for Truncate and Drop operations

[linq2dbot]

Test baselines changed by this PR. Don't forget to merge/close baselines PR after this pr merged/closed.